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Sternum

Sternum

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Encyclopedia
The sternum or breastbone is a long flat bony plate shaped like a capital "T" located anteriorly to the heart in the center of the thorax
Chest
The chest is a part of the anatomy of humans and various other animals. It is sometimes referred to as the thorax or the bosom.-Chest anatomy - Humans and other hominids:...

 (chest). It connects the rib bones
Rib
In vertebrate anatomy, ribs are the long curved bones which form the rib cage. In most vertebrates, ribs surround the chest, enabling the lungs to expand and thus facilitate breathing by expanding the chest cavity. They serve to protect the lungs, heart, and other internal organs of the thorax...

 via cartilage
Cartilage
Cartilage is a flexible connective tissue found in many areas in the bodies of humans and other animals, including the joints between bones, the rib cage, the ear, the nose, the elbow, the knee, the ankle, the bronchial tubes and the intervertebral discs...

, forming the anterior section of the rib cage
Human rib cage
-See also:*Terms for bones*Terms for anatomical location*Articulation of head of rib-References:* Clinically Oriented Anatomy, 4th ed. Keith L. Moore and Robert F. Dalley. pp. 62–64...

 with them, and thus helps to protect the lungs
Human lung
The human lungs are the organs of respiration in humans. Humans have two lungs, with the left being divided into two lobes and the right into three lobes. Together, the lungs contain approximately of airways and 300 to 500 million alveoli, having a total surface area of about in...

, heart
Human heart
The human heart is a muscular organ that provides a continuous blood circulation through the cardiac cycle and is one of the most vital organs in the human body...

 and major blood vessels from physical trauma
Physical trauma
Trauma refers to "a body wound or shock produced by sudden physical injury, as from violence or accident." It can also be described as "a physical wound or injury, such as a fracture or blow." Major trauma can result in secondary complications such as circulatory shock, respiratory failure and death...

. Although it is fused, the sternum can be sub-divided into three regions: the manubrium, the body, and the xiphoid process.

The sternum is sometimes cut open (a median sternotomy
Median sternotomy
Median sternotomy is a type of surgical procedure in which a vertical inline incision is made along the sternum, after which the sternum itself is divided, or "cracked"...

) to gain access to the thoracic contents when performing cardiothoracic surgery
Cardiothoracic Surgery
Cardiothoracic surgery is the field of medicine involved in surgical treatment of diseases affecting organs inside the thorax —generally treatment of conditions of the heart and lungs .-Cardiac / Thoracic:...

.

Overview


The sternum is an elongated, flattened bone, forming the middle portion of the anterior wall of the thorax. The superior end supports the clavicles (Collar bones), and its margins articulate with the cartilages of the first seven pairs of ribs. Its top is also connected to the Sternocleidomastoid muscle
Sternocleidomastoid muscle
In human anatomy, the sternocleidomastoid muscle , also known as sternomastoid and commonly abbreviated as SCM, is a paired muscle in the superficial layers of the anterior portion of the neck...

. It consists of three main parts, listed superior to inferior:
  • Manubrium
    Manubrium
    The manubrium or manubrium sterni is the broad, upper part of the sternum. Located ventrally with a quadrangular shape, wider superiorly and narrower inferiorly, it articulates with the clavicles and the first two ribs.-Borders:The superior border is the thickest and presents at its center the...

  • Body of sternum
    Body of sternum
    The body of the sternum , considerably lengthier, narrower, and thinner than the manubrium, attains its greatest breadth close to the lower end.- Surfaces :...

     (gladiolus)
  • Xiphoid process
    Xiphoid process
    The xiphoid process, or xiphisternum or metasternum, is a small cartilaginous process of the lower part of the sternum which is usually ossified in the adult human. By age 15 to 29, the xiphoid usually fuses to the body of the sternum with a fibrous joint. Unlike the synovial articulation of major...



In its natural position, the inclination of the bone is oblique from above, downward and forward. It is slightly convex in front and concave behind; broad above, shaped like a "T", becoming narrowed at the point where the manubrium joins the body, after which it again widens a little to below the middle of the body, and then narrows to its lower extremity. Its average length in the adult is about 17 cm, and is rather longer in the male than in the female.

In early life its body is divided in four segments, called sternebrœ (singular: sternebra).

Structure


The manubrium (ma-NOO-bree-um) is the broad superior portion of the sternum. The suprasternal (jugular) notch is medially located at the superior end of the manubrium. You can feel this notch between your two clavicles (collarbones). Located superiorly and laterally are the right and left clavicular notches.

The body
Body of sternum
The body of the sternum , considerably lengthier, narrower, and thinner than the manubrium, attains its greatest breadth close to the lower end.- Surfaces :...

, or gladiolus, is the longest part of the sternum. The sternal angle
Sternal angle
The sternal angle or 'angle of Louis', from the Latin angulus Ludovici is the anterior angle formed by the junction of the manubrium and the body of the sternum in the form of a secondary cartilaginous joint . This is also called the manubriosternal joint or Angle of Louis...

 is located at the point where the body joins the manubrium. The sternal angle can be felt at the point where the sternum projects farthest forward. However, in some people the sternal angle is concave or rounded. During physical examinations, the sternal angle is a useful landmark when counting ribs because the second rib attaches here.

Located at the inferior end of the sternum, is the pointed xiphoid (ZIF-oyd) process. Improperly performed chest compressions during cardiopulmonary resuscitation
Cardiopulmonary resuscitation
Cardiopulmonary resuscitation is an emergency procedure which is performed in an effort to manually preserve intact brain function until further measures are taken to restore spontaneous blood circulation and breathing in a person in cardiac arrest. It is indicated in those who are unresponsive...

 can cause the xiphoid process to snap off, driving it into the liver which can cause a fatal hemorrhage.

The sternum is composed of highly vascular
Vascular
Vascular in zoology and medicine means "related to blood vessels", which are part of the circulatory system. An organ or tissue that is vascularized is heavily endowed with blood vessels and thus richly supplied with blood....

 tissue, covered by a thin layer of compact bone which is thickest in the manubrium
Manubrium
The manubrium or manubrium sterni is the broad, upper part of the sternum. Located ventrally with a quadrangular shape, wider superiorly and narrower inferiorly, it articulates with the clavicles and the first two ribs.-Borders:The superior border is the thickest and presents at its center the...

 between the articular facets for the clavicles.

Articulations


The superior seven costal cartilages articulate with the sternum forming the costal margin
Costal margin
The costal margin, sometimes referred to as the costal arch, is the medial margin formed by the false ribs and one true rib -- specifically, from the seventh rib to the tenth rib....

 anteriorly. The right and left clavicular notches articulate with the right and left clavicles, respectively. The costal cartilage of the second rib articulates with the sternum at the sternal angle making it easy to locate.

The transversus thoracis muscle
Transversus thoracis muscle
The transversus thoracis lies internal to the thoracic cage, anteriorly. It is a thin plane of muscular and tendinous fibers, situated upon the inner surface of the front wall of the chest...

 is innervated by the intercostal nerve and superiorly attaches at the posterior surface of the lower sternum. Its inferior attachment is the internal surface of costal cartilages two through six and works to depress the ribs.

Fractures of the sternum



Fractures of the sternum
Sternal fracture
A sternal fracture is a fracture of the sternum , located in the center of the chest. The injury, which occurs in 5–8% of people who experience significant blunt chest trauma, may occur in vehicle accidents, when the still-moving chest strikes a steering wheel or dashboard or is injured by a...

 are rather uncommon. They may result from trauma, such as when a driver's chest is forced into the steering column
Steering column
The automotive steering column is a device intended primarily for connecting the steering wheel to the steering mechanism or transferring the driver's input torque from the steering wheel.-Secondary functions:...

 of a car
Čar
Čar is a village in the municipality of Bujanovac, Serbia. According to the 2002 census, the town has a population of 296 people.-References:...

 in a car accident
Car accident
A traffic collision, also known as a traffic accident, motor vehicle collision, motor vehicle accident, car accident, automobile accident, Road Traffic Collision or car crash, occurs when a vehicle collides with another vehicle, pedestrian, animal, road debris, or other stationary obstruction,...

. A fracture of the sternum is usually a comminuted fracture. The most common site of sternal fractures is at the sternal angle
Sternal angle
The sternal angle or 'angle of Louis', from the Latin angulus Ludovici is the anterior angle formed by the junction of the manubrium and the body of the sternum in the form of a secondary cartilaginous joint . This is also called the manubriosternal joint or Angle of Louis...

.
Some studies reveal that repeated punches or continual beatings, sometimes called "sternum punches", to the sternum area have also caused fractured sternums. Those are known to have occurred in contact sports such as rugby and football.
Sternum fractures are frequently associated with underlying injuries such as pulmonary contusion
Pulmonary contusion
A pulmonary contusion is a contusion of the lung, caused by chest trauma. As a result of damage to capillaries, blood and other fluids accumulate in the lung tissue. The excess fluid interferes with gas exchange, potentially leading to inadequate oxygen levels...

s, or bruised lung tissue.
A somewhat rare congenital condition of the sternum is a sternal foramen, a single round hole in the sternum that is present from birth and usually is off-centered to the right or left, commonly forming in the 2nd, 3rd, and 4th segments of the sternum body. Sternal foramens can often be mistaken for bullet holes.

See also

  • Ossification of sternum
    Ossification of sternum
    The sternum originally consists of two cartilaginous bars, situated one on either side of the median plane and connected with the cartilages of the upper nine ribs of its own side....

  • Bone terminology
  • Terms for anatomical location
  • Pectus carinatum
    Pectus carinatum
    Pectus carinatum, , also called pigeon chest, is a deformity of the chest characterized by a protrusion of the sternum and ribs. It is the opposite of pectus excavatum.-Causes:...

  • Pectus excavatum
    Pectus excavatum
    Pectus excavatum is the most common congenital deformity of the anterior wall of the chest, in which several ribs and the sternum grow abnormally. This produces a caved-in or sunken appearance of the chest...